1. Field of the Invention
The invention relates to a sensor for contactless detection of wear in a brake lining of a motor vehicle, wherein the wear-induced displacement of the brake lining relative to the brake caliper or the displacement range of a mechanical or electromechanical adjuster for compensating the brake lining wear is determined for a subsequent electronic analysis device and/or warning device.
2. Description of the Background Art
Such systems are known. Thus, DE 101 32 968 A1 discloses a potentiometer with a straight-line resistive track in which a wear-induced displacement of the brake lining is communicated to the resistive track by linear motion. A disadvantage in this system is that the communication is not “contactless,” which is to say that the motion is communicated directly to the potentiometer by mechanical coupling. This mechanical coupling has the result that separating the sensor from the brake caliper in order to service the brake or replace a lining is very complicated, if it is possible at all, and may require readjustment of the sensor.
In contrast, DE 196 37 394 discloses a “contactless” measurement of brake lining wear. Thus, a Hall sensor is provided on a brake caliper and a magnet is provided on the brake piston. The relative linear displacement between the piston and brake caliper caused by the wear is determined by means of the resulting change in the magnetic field. While a “contactless” measurement is indeed disclosed, it is not proposed in order to simplify maintenance.
Both the embodiments described above have in common that the wear-induced linear displacement between the brake lining and brake caliper is determined directly. This requires a particularly high detection precision of the sensor and the associated measurement mechanism in order to be able to reliably detect the comparatively small wear displacement.
In order to increase the detection precision, it is thus advantageous to measure the brake lining wear by the means that a transmission is present that converts the linear motion of the wear-induced brake lining displacement into a rotary motion that can be detected with better resolution. To this end, it is possible to attach the sensor to the adjusters that are customarily present, since the customary adjusters are generally based on a rotary motion of a motor being translated, in particular geared down, into a linear displacement of the brake lining. In this context, the practitioner of the art encounters the problem that the limited range of measurement of a potentiometer or Hall sensor makes detection very difficult or impossible. In this regard, DE 103 05 702 discloses an electric-motor-driven displacement or adjustment of a brake lining, wherein the associated actuating motor has a decoder disk with multiple alternating magnetized areas on one of its shafts for detecting its rotary motion, the motion of said magnetized areas being detected by the switching on and off of multiple Hall sensors, which is to say digitally. Since no detection signal is produced that unambiguously corresponds to the relevant position resulting from the rotary motion, relatively complicated analysis logic is necessary, and complicated readjustment is required during maintenance, in particular after brake lining replacement.